Such an inertization device is known in principle from the prior art. For example, German Patent Specification DE 198 11 851 C2 describes an inertization device for reducing the risk of fire and for extinguishing fires in enclosed spaces. The known system is configured to decrease the oxygen concentration within an enclosed room (hereinafter called “protective room”) to a base inertization level, which can be preset in advance, and in the event of a fire to rapidly further decrease the oxygen concentration to a specific full inertization level, thereby enabling the fire to be effectively extinguished with the smallest possible storage capacity required for inert gas tanks. For this purpose, the known device has an inert gas system that can be controlled via a control unit, and a supply pipe system that is connected to the inert gas system and to the protective room, via which the inert gas provided by the inert gas system is supplied to the protective room. The inert gas system can be either a steel cylinder battery, in which the inert gas is stored in compressed form, a system for generating inert gases, or a combination of these two options.
The inertization device of the type initially mentioned is a system for reducing the risk of fire and for extinguishing fires in the monitored protective room, whereby a sustained inertization of the protective room is used to prevent and/or to fight fires. The functioning method of the inertization device is based upon the knowledge, that in enclosed spaces, the risk of fire can be countered by reducing the oxygen concentration in the relevant area in a sustained manner to a level of, for example, approximately 12 vol.-% under normal conditions. At this oxygen concentration, most combustible materials can no longer burn. The main areas of application include especially ADP areas, electrical switching and distribution spaces, enclosed facilities, and storage areas containing high-value commercial goods.
The prevention and/or extinguishing effect that results from the inertization process is based upon the principle of oxygen displacement. As is known, normal environmental air is made up of 21 vol.-% oxygen, 78 vol.-% nitrogen and 1 vol.-% other gases. In order to effectively decrease the risk that a fire will start in a protective room, the oxygen concentration is decreased in the relevant space by introducing inert gas, such as nitrogen. With respect to extinguishing fire in most solid materials, it is known, for example, that an extinguishing effect is generated when the oxygen ratio drops below 15 vol.-%. Depending upon the combustible materials that are present in the protective room, a further decrease in the oxygen ratio, for example to 12 vol.-%, may be necessary. In other words, with a sustained inertization of the protective room to a so-called “base inertization level,” at which the oxygen ratio in the air inside the room is decreased, for example to below 15 vol.-%, the risk of a fire igniting inside the protective room can be effectively decreased.
The term “base inertization level” used herein is generally understood to refer to an oxygen concentration in the air inside the protective room that is reduced as compared with the oxygen concentration of normal environmental air, whereby, however, in principle this reduced oxygen concentration presents no danger of any kind to persons or animals from a medical standpoint, so that they are still able to enter the protective room—under certain circumstances, with certain protective measures. As was already mentioned, the establishment of a base inertization level which, in contrast to the so-called “full-inertization level”, need not correspond to an oxygen ratio that is decreased such that fire is effectively extinguished, serves primarily to reduce the risk of a fire igniting within the protective room. The base inertization level corresponds to an oxygen concentration of, for example, 13 vol.-% to 15 vol.-% —depending upon the circumstances of the individual case.
In contrast, the term “full inertization level” refers to an oxygen concentration that is further reduced as compared with the oxygen concentration of the base inertization level, and at which the flammability of most materials is already decreased so far, that they are no longer capable of igniting. Depending upon the fire load present inside the protective room, the full inertization level generally ranges from 11 vol.-% to 12 vol.-% oxygen concentration.
Although, in principle, the reduced oxygen concentration which corresponds to the base inertization level in the air inside the protective room presents no danger to persons and animals, so that they can safely enter the protective room, at least for short periods of time, without significant hardships, for example without gas masks, certain nationally stipulated safety measures must be adhered to in entering a room that has been permanently inertized to a base inertization level, because, in principle, a stay in a reduced oxygen atmosphere can lead to an oxygen deficiency, which under certain circumstances can have physiological consequences in the human organism. These safety measures are stipulated in the respective national regulations, and are dependent especially upon the level of reduced oxygen concentration that corresponds to the base inertization level.
In Table 1 below, these effects on the human organism and on the combustibility of materials are presented.
In order to adhere to the safety measures with regard to the passability of the protected room stipulated in the national regulations, which become stricter as the oxygen ratio in the air inside the protective room decreases in a simple manner that is especially easy to implement, it would be conceivable for the purpose of and for the duration of passage into the room to raise the sustained inertization of the protective room from the base inertization level to a so-called passability level, at which the prescribed safety requirements are lower and can be met without major inconvenience.
TABLE 1Oxygen ratioEffect on theinside theEffect on thecombustibilityprotective roomhuman organismof materials 8 vol.-%Risk to lifeNot combustible10 vol.-%Discernment andNot combustiblesensitivity topain diminish12 vol.-%Fatigue, elevationDifficult to igniteof respiratoryvolume and pulse15 vol.-%NoneDifficult to ignite21 vol.-%NoneNone
For example, in a protective room that under normal conditions is permanently inertized to a base inertization level of, for example, 13.8 to 14.5 vol.-%, at which, according to Table 1, an effective suppression of fire can be achieved, it would make sense to reduce the oxygen ratio to a passability level, for example of 15 to 17 vol.-%, when it is to be entered, for example for maintenance purposes.
From a medical point of view, a temporary stay in an oxygen atmosphere that has been reduced to this passability level is safe for persons who have no cardiac, circulatory, vascular or respiratory illnesses, so that the respective national regulations governing this require no, or only minor, additional safety measures.
Ordinarily, raising the inertization level established inside the protective room from the base inertization level to the passability level is accomplished via a corresponding control of the inert gas system. In that regard it is practical, especially for economic reasons, to consistently maintain the inertization level established inside the protective room at the passability level during passage into the protective room (for instance with a corresponding control range), in order to minimize the quantity of inert gas to be introduced back into the protective room once the visit has been completed, in order to reestablish the base inertization level. For this reason, the inert gas system should also be generating and/or providing inert gas during the period of passage into the protective room, so that the inert gas will be correspondingly supplied to the protective room, in order to maintain the inertization level there at the passability level (optionally with a specific control range).
In the process n it is noted, that the term “passability level” used herein refers to an oxygen concentration in the air inside the protective room which is reduced in comparison with the oxygen concentration of the normal surrounding air, in which the respective national regulations require no, or only minor, supplementary safety measures for entering the protective room. As a rule, the passability level corresponds to an oxygen ratio in the air inside the room that is higher than a base inertization level.